With age, characteristic changes occur in the central third of the face.  A youthful midface is characterized by prominent cheeks and a smooth transition between the lower eyelid and cheek. Structural, soft tissue, and skin changes develop as wrinkles and creases, progressive ptosis, and general atrophy of the structures.
Pessa confirmed the changes seen in the bony structures of the face, and these include a downward migration of cephalometric points.  The downward migration manifests as a change in soft tissue volume. The effects of gravity and repeated animation of the face also directly affect the soft tissue that overlies the mimetic musculature.
The results of magnetic resonance imaging (MRI) evaluations have helped to determine that the mimetic muscles themselves remain intact; however, the attachment to the overlying soft tissue and skin changes. The repeated action of smiling results in deepening of the nasolabial fold at the point at which the superficial musculoaponeurotic system (SMAS) inserts into the dermis.
Basic Neurovascular Anatomy
The rich arterial supply of the midface is secondary to the musculocutaneous perforators branching from the facial artery. In addition, several arterial anastomotic links from the superficial temporal artery and the ophthalmic artery increase the arterial inflow.  Within the region of the central third of the face are several significant arterial branches, including the angular artery, superior and inferior labial arteries, and infraorbital branch. This redundant and well-developed arterial system allows aggressive flap elevation of the midface, in most cases, with a minimal risk of skin slough. [4, 5, 6]
In the submental region, the submental perforator artery has been identified as a potential cause of bleeding during facial rejuvenation.  This branch of the submental artery has been identified by Hwang et al as emerging halfway between the gonion and menton. 
The facial nerve exits the skull just inferior to the tragus of the ear. (See the image below.) The proximal branches course deep to the superficial musculoaponeurotic system (SMAS). The frontal branch extends along a line 0.5 cm below the tragus to 1.5 cm above the lateral brow and becomes more superficial at the level of the zygoma. The frontal branch has little cross-innervation compared with the buccal and zygomatic branches of the facial nerve.  Unlike the cervical branch, it transitions from a deep plane to a more superficial plane. The great auricular nerve is a sensory branch.
The buccal and zygomatic branches pass deep to the SMAS within the parotid gland until the terminal branches pass superficially to innervate the mimetic muscles anterior to the parotid gland. The mandibular branch usually remains superior to the inferior border of the mandible until it reaches the facial artery crossing the mandibular margin.  The terminal branches distal to the facial artery are uniformly inferior to the mandibular border.
Sensory innervation is provided by the supraorbital, infraorbital, and mental nerves in the medial portion of the face. The great auricular nerve originates from the cervical plexus and passes inferiorly to cross the sternocleidomastoid muscle 6.5 cm inferior to the auditory canal. The nerve passes deep to the skin and SMAS along the path of the external jugular vein. [10, 11]
Malar Fat Pad
In a youthful midface, the malar fat pad (outlined in the image below) is located over the zygomatic bone. The triangular pad lies along the edge of the nasolabial fold. Its upper border covers the orbital rim and the orbital part of the orbicularis oculi. The lateral border can be identified by drawing a perpendicular line from the lateral canthus down to the triangular apex of the malar fat pad. The malar fat pad is located beneath the skin and subcutaneous fat, but it is superficial to the SMAS and has little significant structural attachment to it. The malar fat pad is fibrous and fatty and is readily distinguishable from the overlying subcutaneous fat.
With advancing age, the malar fat pad slides downward and slightly forward, over the SMAS. Over time, gravity pulls the malar fat pad down off the zygomatic arch and the orbicularis oculi muscle. Because of the malar fat pad's tight adherence to the skin but loose connection to the SMAS, it translocates along the surface of the SMAS to ultimately reside inferior and medial to its prior position. It bulges against the fixed nasolabial crease and creates the illusion of deepening it. The corner of the mouth droops, and the commissure develops a downward orientation. To a lesser extent, this displacement also results in the formation of labiomandibular folds (so-called marionette lines) and jowls.
As a person ages, the malar fat pad slides inferiorly and medially over the SMAS. Ptosis of the malar fat pad also empties the inferior eyelid aesthetic unit of sufficient volume. Correction involves vertical elevation of the malar fat pad to address the midface. [12, 13]
Proper surgical rejuvenation of the face restores the original anatomy and therefore allows a younger, natural appearance that reflects the person's appearance prior to the extended effects of gravity. The vertical repositioning of the malar fat pad is key to restoring a youthful appearance in the adult face.
When assessing the midface for rejuvenation potential, evaluating the lower eyelid and periorbital region is important. Of particular importance is evaluation of the amount of excess skin and periorbital fat herniation. To correct the tissue that has been displaced from the lower lid region, lower blepharoplasty is performed in conjunction with midface rejuvenation.
For this, a small skin-muscle flap is removed from the area extending to the lateral canthus. After removal of at most a minimal amount of fat (sometimes, no fat is removed), a clear 4-0 nylon suture is used to tighten and suspend the preseptal orbicularis oculi muscle. This allows correction of periorbital fatty herniation without the need for aggressive resection, which can lead to hollowing of the orbit. In addition, it tightens the lower lid and reduces the risk of lower lid ectropion. Frost sutures are also used during the first 24 hours to reduce the risk of ectropion.
Superficial Musculoaponeurotic System
The SMAS is the superficial fascia of the face and neck.  More accurately, it is a fibromuscular layer. It extends from the malar region superiorly to become continuous with the galea, inferiorly to become part of the platysma, and laterally to invest in the parotid fascia over the parotid gland. The SMAS is thicker and well attached to the underlying fascia over the proximal masticatory zone and thinner and more separable from the underlying fascia over the distal masticatory zone. (See image below.)
The temporal region the SMAS is described as having 2 layers where it transitions into the superficial temporal fascia or temporalis fascia. Deep to the temporal region of the SMAS lies the superficial temporal artery and frontal branch of the facial nerve.
The SMAS invests the superficial mimetic muscles, including the platysma muscle, orbicularis oculi muscle, occipitofrontalis muscle, zygomatici muscles, and levator labii superioris muscle. It attaches to the skin via ligamentous extensions and is thicker and more distinctly developed at the zygomaticus major muscle.
Sharp dissection performed at the level of the parotid fascia frees up a plane above the deep facial fascia, thereby protecting the facial nerve. Full mobilization of the SMAS can be achieved starting 2-3 cm anterior to the pretragal crease, in front of the anterior border of the masseter muscle. Some reports indicate that the SMAS layer can be elevated as far medial as the nasolabial fold. The SMAS can also be repositioned, partially excised, or plicated as needed to further augment or contour the elevation of the malar fat pad.
Importantly, recognize the key role that tightening the SMAS plays in global facial rejuvenation. However, the SMAS is of more value for improving the lower third of the face than the midface. Tightening the SMAS by any method provides a suitable support framework for platysmal plication. (See also Extended SMAS Facelift.)
Retaining Ligaments and Platysma
The retaining ligaments of the malar fat pad and midface consist of the orbital retaining ligaments and lateral orbital thickening.  The lateral orbital thickening just lateral to the lateral canthus and the lateral orbital retaining ligament along the infraorbital border prevent adequate mobilization of the malar fat pad. Various additional retaining ligaments that compartmentalize the fat of the central third of the face have also been described; however, successful elevation of the malar fat pad depends on proper identification and release of these 2 structures. 
The platysma is invested into the inferior extent of the SMAS. Fat superficial to the platysma can be liposuctioned or directly excised. The platysma can be plicated, suspended with sutures, or even partially excised, as needed, to further define the proper mandibular-neck angle.
The authors' preferred technique for facelifts uses a prehairline incision and subcutaneous dissection plane. The procedure is performed with the patient under general anesthesia. After infiltration with 0.5% lidocaine (Xylocaine) and 1:200,000 epinephrine, the initial incision is made starting 1.5 cm above the lateral eyebrow. This incision is continued in front of the sideburn. It is then continued behind the ear at the level of the tragus after following the earlobe. This approach also allows for excision of a transverse wedge above the ear at the conclusion of the procedure.
Dissection is performed in the subcutaneous plane, superficial to the SMAS and well away from the branches of the facial nerve. The end points of this dissection are critical to the ultimate outcome of the procedure. Superiorly, the dissection should not extend past the lateral eyebrow. Inferiorly, the limit is variable and must be adjusted to account for soft tissue sagging. The inferior area is tapered down to the mandibular-nasal-canthal intersection point. This point is located by drawing a vertical line down from the lateral canthus and a horizontal line across from the base of the nose. Dissection performed past this point risks disrupting the connections between the malar fat pad and the nasolabial fold.
The depth of dissection should be rather superficial in some areas. These include the areas above the lateral portion of the malar fat pad and above the orbicularis oculi muscle.
When proper exposure of the malar fat pad has been accomplished, 2 Allis clamps are used to grasp the pad and elevate it from the edge of the zygoma (see the image below). Repositioning can then be accomplished such that the nasolabial fold is reduced, the jowls are raised, and the corner of the mouth is elevated. Vertical nylon sutures in the superficial temporal fascia at the level of the eyebrows secure the pad in the desired position.
An alternative approach using the same planes of dissection is available through the lower blepharoplasty incision. This approach, while reliable, limits the skin resection and provides a less dramatic elevation of the malar fat pad.